1. Field of the Invention
This invention relates to a display panel for displaying images by utilizing gaseous discharge and more particularly a gaseous discharge display panel for displaying color images.
2. Description of the Prior Art
Nowadays several kinds of gaseous discharge display apparatuses have been developed for output devices of electronic computers. Some of them have been practically used. Recently active studies have been conducted in various fields for developing a new display apparatus for television images. However known display apparatuses have many disadvantages and thus they could not be used as the television image display apparatus. These disadvantages are mainly concerned with an operational characteristic of a discharge unit and luminous characteristics, particularly brightness and luminous efficiencies in case of displaying color images. The former problem is mainly due to a fact that an operational voltage of the discharge units is high and the response speed of the discharge hardly corresponds with a scanning speed of the television standards. This problem can be solved by transferring glow discharge at a rear side of the display part by using the same principle as that used in a dekatron so as to realize a line-simultaneous address device such as a known self-scan panel display device (SSPD). In order to avoid the latter problem great effort has been made. For example in order to improve the brightness and luminous efficiencies, fluorescent materials are provided in the discharge unit and are excited by an ultra-violet ray. However, this latter problem could not be satisfactorily avoided. In particular the low brightness and low efficiency are serious drawbacks in the case of displaying color images even in the above mentioned self-scan panel display device. Therefore it has been earnestly required to obviate the latter drawbacks.
It has been proposed to form the gaseous discharge display panel by a plurality of layers, at one of which is produced an addressing or scanning glow discharge array and wherein another one of which is used for display discharge, and display discharge units at which said glow discharge array are situated are made to discharge more easily than another other display discharge units so as to address positively the particular display discharge unit. In one example of such a gaseous discharge display panel of multi-layer construction each cathode for forming the scanning glow discharge array is made of a strip-shape electrode in which a number of holes are formed at a given interval. A number of such cathodes are arranged in parallel with each other adjacent to an intermediate sheet of an insulating plate in which a number of through holes are formed in a matrix form, these holes being aligned with the small holes in the cathodes. On the rear side of the cathodes are arranged a number of scanning anodes, each of which is formed by a straight wire and is inserted in a trough formed on an inner surface of an insulating rear sheet. These scanning anode wires are arranged in parallel with each other and at right angles with respect to the extending direction of the cathodes. The scanning anode wires are aligned with the small holes of the cathodes and are spaced from the cathodes by a given distance. On the display side of the intermediate sheet are arranged a number of display anodes, each consisting of a straight wire aligned with the small holes of the intermediate sheet. These display anodes are arranged in parallel with each other and at right angles with respect to the extending direction of the strip-shape cathodes. The scanning cathodes also serve as display cathodes which cooperate with the display anodes. On the front side of the display anodes is arranged a front sheet. These sheets are stacked and the peripheries of the assembly are hermetically sealed by means of flits. Inside of the assembly is introduced a gas mainly consisting of neon. In the case of displaying color images by using the above mentioned known display panel, red, blue and green fluorescent materials are applied to an inner surface of each hole formed in the intermediate sheet or fluorescent materials are applied to the inner surface of the front sheet at positions corresponding to the holes of the intermediate sheet. In this case a mixed gas of neon and xenon is used and fluorescent materials are excited by ultra-violet rays produced by gaseous discharge. When a color image is displayed by means of the known gaseous discharge display panel of the above construction, the following drawbacks arise.
1. Since the electric field of a positive column produced at the through hole of the intermediate sheet is week, the intensity of the produced ultra-violet ray is small. The fluorescent materials are mainly exited by the ultra-violet ray from the negative glow formed at the front surface of the cathode and the ultra-violet ray is absorbed by the introduced gas on account of the positions of the fluorescent materials, so that the luminous intensity is low.
2. Due to the construction of the discharge unit the luminescence from the fluorescent material is inspected as a transmitted light or in case of viewing the reflected light only a part thereof is inspected and thus the brightness of displayed images is low.
3. Owing to the construction of the cathodes it is impossible to supply a large discharge current in the normal glow discharge condition, so that the high brightness cannot be obtained even by exciting the fluorescent materials by the ultra-violet ray produced from the discharge. If the larger current than the normal glow discharge is supplied, the chromaticity of the fluorescent materials is extremely deteriorated.
4. Since the discharge units each forming a picture element or dot cannot be arranged with a high density, the good image of high quality could not be displayed.
5. Since it is difficult to connect the discharge units, a large screen display apparatus cannot be easily obtained by composing a plurality of display panels.
6. Since the light of the scanning discharge moving at the rear side of the panel penetrates into the display side, the brightness of a background of images becomes higher and thus the contrast range of the images is made narrow.